A Pilot Study of the Effect of Dietary Fat Type and Amount on Vitamin D3 Absorption

There is evidence that vitamin D has a favorable effect on bone and muscle. Many adults have low blood levels of 25-hydroxyvitamin D (25OHD) and consequently, vitamin D supplements are being widely recommended. The effect of a meal on the absorption of vitamin D is poorly understood. This single blind study will examine whether the amount and type of fat in the meal with which vitamin D is taken influences its absorption. Vitamin D dissolves in fat and so dietary fat may affect its absorption; moreover the type of fat with respect to mono- and poly-unsaturation may also influence absorption. This study should increase our understanding of how best to take vitamin D in order to achieve maximal absorption. Up to 65 healthy older men and women with 25OHDlevels in the insufficient range will be enrolled in order to get 60 completers in this 1-day study. They will randomized to one of three meal groups: high MUFA/PUFA (n=30), low MUFA/PUFA (n=15), or fat-free (n=15). Those in the high MUFA/PUFA group will also be randomized to a single dose of either 1,600 or 50,800 IU of vitamin D. All participants in the other two groups will receive the 50,800 IU dose. They will consume only the three meals provided during the study day. In the morning they will come to the Center for a blood draw, to consume their breakfast meal, and to take their assigned dose of vitamin D (part of which is labeled with the non-radioactive tracer, deuterium to enable direct assessment of vitamin D absorption). They will also complete questionnaires about their diet and health and have a DXA total body scan. They will be given a boxed lunch to eat at noon. They will return to HNRCA for blood draws at 6:00, 8:00, and 10:00 pm. They will have dinner at HNRCA after the 6:00 pm blood draw. They finish the study after the final blood draw. Participants who receive the higher dose of vitamin D, 50,800 IU, will be asked not to take more than 400 IU of vitamin D or 1000 mg per day of supplemental calcium or attend tanning salons for the month after completing the study, in order to minimize any risk of symptoms from the vitamin D. Blood draws include screening visit 20 cc, morning visit 15 cc, and three evening blood draws of 15, 15, and 15 cc, respectively, total 80 cc.